I. Field of the Invention
The present invention relates generally to a coiling machine for coiling a continuous paper web.
In the coiling of webs, coil hardness plays a role for subsequent further processing. Particularly in the case of paper webs, it is very important that the paper coil hardness over the entire roll diameter develops in a certain way. In general, the coil hardness will decrease from a specific initial value to a final value. The decrease will be as uniform as possible from the first to the last layer. It will have a specific gradient, i.e., not too large and not too small. The course of coil hardness will in no case have abrupt steps, e.g., a sudden decrease.
These conditions are obtained only if certain measures are taken. If nothing is done, then with increasing roll diameter, the linear pressure between the roll and the king large roll or the king large rolls becomes increasingly greater, and thus so does the coil hardness.
In order to avoid this, compressed air is applied in the machines according to the overall concept of the present invention, which enters through the compressed air connection into the pressure-tight chamber under the paper coil. Quantities of air or air pressure can be controlled according to the increasing weight of the coil. It is also possible to divide the chamber over its length--i.e., over the web width--into individual chambers, and to provide each of these individual chambers with a pressure connection. In this way, the sagging of the coil can also be equilibrated.
Further, so-called riding rollers are applied, which are arranged with parallel axes to the king rolls. Pressure is applied to the roll with the latter riding rollers. The pressure is controlled, whereby it is large initially and becomes smaller with increasing roll weight.
The riding roller thus permits influencing linear pressure and thus the coil hardness and controlling these in the desired way. However, if it is desired to produce a roll of very large diameter, then the linear pressure in the final phase of coiling is very high. Because of this, the coil tension increases, so that cracks may occur in the web or crepe-like folds may form.
Other measures for influencing the coil hardness consist of the fact that the load of the roll coil is distributed onto the individual king rolls. For this purpose, king rolls of the same diameter were arranged in different horizontal planes or king rolls of different diameter were used. Further, it is known that for coiling onto a king roll of smaller diameter, al harder coil is obtained than when coiling onto a king roll of larger diameter.
II. Description of the Prior Art
A coiling machine which has two king rolls of equal size is known from DE-DM 7,310,606. One of these king rolls can be lowered during the coiling process from an upper position above the horizontal plane of the axis of the other king roll at the beginning of the coiling process. A rigidly wound core can be obtained initially by this lowering of the roll.
U.S. Pat. No. 2,461,387 describes a coiling machine, which has two driven king rolls of different diameter; the king roll of smaller diameter is provided with a coating with a larger coefficient of friction and is driven at a higher speed than the other king roll. In this way, a tensile stress is exercised on the outer layer of the web.
DE OS 2,757,247 (not examined) concerns a coiling machine with king rolls of the same size diameter. The control of coil hardness is made by changing the distance between the king rolls.
DE Patent 678,585 describes a coiling machine with two king rolls, the first of which has a hard jacket and the second has a soft jacket. The axes of both rolls are found in one and the same horizontal plane.
DE 3,839,244 describes a coiling machine with three king rolls. The first of these king rolls is stationary, while the two subsequent king rolls vary in their position and are wrapped by a support strip. The coil hardness over the roll diameter can be controlled by the support strip as well as by the change in position of the second and third king rolls. Thus the support strip creates a support surface that is as large as possible for purposes of decreasing the surface load. This coiling machine is extremely expensive. It also has a particularly serious disadvantage: as soon as the paper roll has grown to the point where it is primarily supported by the support strip, a violent swinging of the support strip occurs, so that the paper roll begins to "dance" and thus can be catapulted from the bed.
It has also been proposed for a coiling machine with two king rolls to produce the jackets of these two rolls from rubber. The king rolls have the same diameter and the jackets have the same rubber hardness. However, this design or configuration also leads to a swinging and floating of the paper roll.
EP 0 157,062 B1 describes a coiling machine with two king rolls and one riding roller. The jacket surfaces of all of these rolls are formed from a number of individual fluid chambers, which are arranged axially next to one another and which form the entire jacket surface of the respective rolls upon impact of their individual jacket surfaces. The support behavior of such a roll is, of course, viewed as nonuniform, due to the number of collisions above the web width.
The invention proceeds from DE 3,121,039 C3, in which two king rolls are provided, whereby the two king rolls are arranged such that-at least during a specific operating phase-the central axis of one of the king rolls lies under the central axis of the other king roll. In this preliminary publication, the question remains of which of the two king rolls, i.e., the one with the paper web wound around it or the one which is not wound, lies on the bottom.
Finally, a coiling machine is known from EP 0 562,266 A1, in which the upper vertex of the "harder" king roll lies above the vertex of the "softer" king roll. Thus the paper web is guided up to the coiling bed from below between the two king rolls and is wound around the "harder" king roll, which is very important according to that patent application.
Indeed, partial problems of the coiling process have been resolved with all of these known coiling machines. However, none of these machines is fully satisfactory with respect to a controllable coil hardness that is free of objection and with respect to the maximally obtainable coil diameter. In particular, it is desired to increase the obtainable coil diameter still more than has been possible previously, without causing a bursting of the outer coil layers. A particularly unpleasant problem, which has not been previously resolved, is the entrainment of air between the individual layers of the coil. This problem has previously not been resolved in a satisfactory manner. For coiling machines in general, and particularly for the coiling machine of the present invention, such a problem would be particularly unpleasant in its appearance.